1. Field of the Invention
This invention relates in general to braking systems and, more particularly, to an interlock system that is easily retrofitted on existing vehicle systems or buses or can be adapted for incorporation as original equipment. This system allows for the installation of a simple auxiliary brake control device that controls only a single circuit while maintaining a high degree of confidence of warning to the driver should the system malfunction.
2. Discussion of the Art
Presently, some state laws require that an operator park a bus during passenger pickup. This necessitates that the operator or driver actuate a park brake, for example, pulling an actuating lever to apply a park brake. Repetitively actuating and deactuating the park brake can cause extreme fatigue to the driver and also frequent actuation requires durable components in the air brake system.
It is known in the industry, for example, as shown and described in U.S. Pat. No. 4,838,617, to interlock brakes with operation of the door. When the door is opened, the brakes are applied and cannot be released while the door remains opened. As taught in U.S. Pat. No. 4,838,617, a solenoid is energized and shifts a plunger to a blocking position in response to a door being opened. A valve maintains pressure in the brake line and prevents release of the brakes even if actuating pressure on the brake pedal is released. Once the door is closed, the solenoid is deenergized and the brakes are released.
Other systems, for example, as taught in U.S. Pat. No. 4,200,167, provide an interlock between the door handle of a bus and a series of switches, such as a brake light switch, gear shift, and a driver control switch before the door is permitted to open.
It is suggested by the present applicant that a safe course of action can be achieved by urging the driver to stay seated with his foot on the brake pedal during a door open state. In other words, it is not necessary to actuate the park brakes as long as the driver remains seated with his foot depressing the foot pedal to effect a normal service brake application, although the driver should be rewarded if a park brake application is made. It is deemed desirable to have the driver cause a service brake application to both the drive and steer axles and be in a position to undertake further action if necessary. It is further desirable to provide a system that monitors the brake application and provides an alarm or signal if certain requirements are not met.
Moreover, retrofitting existing brake systems for buses is often a tedious task. Different original equipment manufacturers (OEMs) have different pneumatic brake systems. These systems are relatively complex since they provide service braking to drive and steer axles, spring park brakes, and emergency systems that use the spring brakes if rear axle service brake capability is lost. Thus, a simple, easy to install retrofit system that does not require a high level of air system knowledge is desirable.
The present invention contemplates a new and improved apparatus and method that overcomes the above-referenced problems and others and provides a simple, effective solution which can be easily retrofitted in existing systems and integrally incorporated in OEM systems.
More particularly, an interlock assembly is provided between a bus door and service brakes so that the service brakes are automatically applied under selected conditions. An alarm associated with an autobrake assembly is responsive to at least one of inadequate pressure for service brake application and insufficient service brake application.
The system is activated in response to turning on the flashing caution lights and opening the bus door.
A pressure indicator monitors application of the parking brakes to deactivate the system once the park brakes are actuated.
A low pressure indicator is actuated in response to a low pressure system and activates the alarm.
Similarly, a pressure indicator monitors pressure delivered from a foot valve to actuate the alarm if there is an indication that the service brakes are not being applied sufficiently.
A principal advantage of the invention is realized by urging the driver to stay seated when the caution lights have been turned on and the door opened so that a normal service brake application is used.
Another advantage of the invention resides in the ability to easily retrofit the system into existing bus brake systems.
Still another advantage of the invention is the ability to provide increased confidence of warning the driver should a system malfunction and protect against misuse or failure of the system through a brake application monitoring device.
Yet another advantage is the reward provided to the driver in disabling the system, including the alarm, if the park brake is applied.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.